Road Science: Top 5 Trends of 2010

Trying to identify major trends and developments that could affect the way highway and bridge construction is done in the next year is something of a challenge at best. But there are some activities that suggest they may impose themselves on, or begin to influence, the process.

1. The stimulus and the TIGER: floatation devices

Stimulus money will continue to affect the way state DOTs operate.

The American Recovery and Reinvestment Act of 2009 (ARRA) economic stimulus law not only has benefited American roadbuilders, spurring rapid road reconstruction from coast-to-coast, but it has kept state DOTs from having to slash their budgets. Its effect will continue into 2010.

According to Federal Highway Administration data (FHWA), across the United States, state DOTs are meeting the act’s tight timeline for obligating their transportation funds, and nearly 4,000 ARRA-financed projects valued at $11 billion are now under construction in the United States.

Also potentially sustaining work through 2010 is the newer Transportation Investment Generating Economic Recovery (TIGER) discretionary grant program. Under TIGER, up to $1.5 billion is available through Sept. 30, 2011, for the secretary of transportation to make grants on a competitive basis for capital investments in surface transportation infrastructure. The response to TIGER was overwhelming; the U.S. DOT received $56.6 billion in project funding requests for the $1.5 billion TIGER discretionary grant program.

“In FY 2009 and FY 2010, federal stimulus funds prevented state spending from falling even more than it would have without the funds,” said Joung H. Lee, associate director for finance and business development, American Association of State Highway and Transportation Officials (AASHTO), on Oct. 14.

But danger looms for FY 2011, Lee said. “Many states say they are looking at a cliff in 2011 because they know ARRA funding will be gone, and they do not expect state revenue performance to rebound strongly enough to make up the difference,” he said.

“Without a doubt, the stimulus has helped keep my company afloat during one of the most difficult economic periods our industry has ever experienced,” Gallagher testified on behalf of the American Road and Transportation Builders Association (ARTBA). Gallagher has benefited from eight new transportation improvement projects that helped save 260 jobs, and create 30 new ones,

The impact of the ARRA is even more evident when looking at new highway contract awards, Gallagher said. During the first four months of 2009, state and local transportation departments awarded $2.1 billion fewer contracts for highway and bridge construction projects than during the same months of 2008, reflecting recession-driven cuts to state and local highway funding.

Since that time, however, in the period between May and August, the value of new contracts for highways and bridges had exceeded 2008 by almost $4 billion, with the ARRA more than offsetting state and local budgetary difficulties. The additional work has allowed transportation contractors to sustain and add to their workforce, Gallagher said.

“The proof is in the numbers,” said Butch Brown, executive director of the Mississippi DOT in early September. As of July, he said, the Mississippi DOT has spent nearly $2 million dollars on payroll. “That money is going straight into the pockets of hundreds of construction workers so they can make mortgage payments, buy groceries, and pay for back to school supplies and clothing,” Brown said.

Dan Flowers, executive director of Arkansas State Highway and Transportation Department, said that the majority of the state’s projects are being built in ‘economically depressed areas,’ which benefits those looking for work. “We’re putting people to work in every corner of our state,” he said.

John Horsley, AASHTO executive director, notes that ,”States are delivering projects on time and many cases under budget. “Now it’s up to Congress to keep the momentum going by passing a new six-year highway and transit authorization bill,” Horsley said.

2. New HMA layer coefficient means thinner layers, more pavement for the same budget

Based on research sponsored by the Alabama Department of Transportation and others, revised structural coefficient of hot mix asphalt will enable thinner lifts of asphalt without sacrificing strength, making state and local road bridges go farther. Photo courtesy of Tom Kuennen

New research refining or “recalibrating” the structural coefficient of asphalt layers is letting the Alabama DOT decrease its hot mix asphalt overlay thicknesses by nearly 19 percent. The new data allow the DOT to place thinner asphalt pavements with the same load-carrying performance as its existing design, allowing more square yards of asphalt pavement to be placed within the same budget, beginning in 2010.

The effect will be more lane miles of asphalt overlay in the state placed with the same budget, and the benefits will apply to other states, counties and cities as well.

The new research from the National Center for Asphalt Technology (NCAT) at Auburn University in Alabama, Recalibration of the Asphalt Layer Coefficient, by Kendra Peters-Davis and Dr. David H. Timm, P.E., was published in August and establishes that in the age of Superpave and other advanced pavement designs, current asphalt layers are stronger structurally than layers used during the AASHO Road Tests of 1958-1960.

One of the main parameters in an asphalt pavement design system is the asphalt layer structural coefficient. The structural coefficient is an index that expresses the structural contribution of the asphalt layer(s) relative to all the other layers.

Based on research from the 1956 AASHO Road Tests, the existing asphalt layer structural layer coefficient value used by Alabama and many other states has been 0.44. The new research incorporates actual performance of modern materials and designs at the National Center for Asphalt Technology (NCAT) Test Track at Auburn University, and has resulted in a new structural layer coefficient value of 0.54.

From a practical standpoint, this permits a thinning of a pavement by about 18.5 percent while still getting the same load-bearing performance as before. Beginning next year, the resulting savings will be used to expand Alabama’s overlay program by a like amount.

“In our recent NCAT test sections, we evaluated the structural layer coefficient that we used in our existing design procedure,” said Mike Harper, P.E., assistant chief engineer for operations, Alabama DOT. “The result of the study was the recommendation that we could comfortably go from 0.44 to 0.54 with our structural layer coefficient in our design procedure. That means, for most of our new pavements, an 18 percent reduction in the total build-up, and an 18 percent reduction in overlay thickness for existing asphalt pavements, which is a tremendous savings for us. We will use that savings to pave more miles.”

The Alabama DOT will implement the new pavement value in its road program in its 2010 budget. As the new fiscal year started Oct. 1, this means that the state will benefit from the road cost savings almost immediately.

“Our resurfacing budget is approved each year,” said Larry Lockett, P.E., state materials and tests engineer, Alabama DOT. “This means that our resurfacing budget will go 18 percent farther than it has in the past. We will be able to pave more roads, more lanes, more miles, because of this 18 percent saving.”

As the economic stimulus package provided about a 40- to 50-percent increase in Alabama’s resurfacing program throughout two years, this 18 percent savings will further leverage those funds to benefit Alabama’s roads and economy.

The research will be publicized by the National Asphalt Pavement Association in the January/February 2010 issue of HMAT Magazine, and the actual NCAT report is available online. To download NCAT Report 09-03, Recalibration of the Asphalt Layer Coefficient, visit www.eng.auburn.edu/center/ncat/reports/rep09-03.pdf.

3. Electricity can be generated by road traffic

In early October, Israeli scientists announced they had achieved a breakthrough in alternative energy, by generating electricity from road traffic. The technology was developed by Innowwattech Ltd., and Israel National Roads Company Ltd. and the Technion Israel Institute of Technology participated in the trial.

The trial proved, for the first time in the world, how electricity can be obtained from generators installed beneath a road’s asphalt layer. Following a successful trial on a short section, the research it will be expanded to several 1 kilometer stretches of one of Israel’s main north-south traffic arteries.

The generators are placed at a depth of 1.9 inch beneath the upper asphalt layer of a road. Piezoelectric materials convert mechanical energy generated from a vehicle’s weight into electricity. Drivers feel no change in the road. Regular vehicle traffic can generate 2,000 watts per hour. The electricity is accumulated in batteries placed along the side of the road.

A change in contract proposed by a road contractor is causing the Utah DOT to look at the use of precast concrete pavement on a heavily traveled Interstate route.

“Precast concrete pavement systems have been shown to accelerate construction time and be economically feasible, while still maintaining the quality of conventional repair methods,” said Ken Berg of the Utah DOT Research Division.

Utah DOT in spring of 2009 advertised a concrete pavement rehabilitation project for I-15 near Clearfield, between Ogden and Salt Lake City. The successful bidder, B. Jackson Construction & Engineering, Inc., proposed use of precast concrete paving slabs, as they now are called. The proprietary system used was the Fort-Miller Super-Slab system, supplied by Mountain West Precast. Utah DOT approved the selection and construction began in March 2009.

The application unfolded against the backdrop of the AASHTO Technical Implementation Group Lead States Team for Precast Concrete Paving Slabs.

“Precast concrete panels for pavement applications is one such technology that should be added as a supplement to the pavement designer’s toolbox of treatment alternatives,” according to the TIG.

The TIG states that new products, emerging technologies and innovative construction practices should not sacrifice quality, durability and long-term performance; provide a means of accelerating the construction scheduling and sequencing; reduce congestion delays caused by excessive construction work zone time frames; and be economically feasible. “It is our belief that when precast paving elements are properly selected as a pavement or repair treatment, all of these beneficial characteristics are attainable,” the TIG. Its work will have ramifications for road builders and owners as 2010 unfolds.

Use of polymer rebar could supplant reinforcing steel in continuously reinforced concrete pavements, if research now underway affirms its use. The 2009 research circular, Evaluating the Use of Fiber-Reinforced Polymer Bars in Continuously Reinforced Concrete Pavement, a product of the FHWA’S Concrete Pavement Technology Program (CPTP), reviewed their status.

Continuously reinforced concrete pavement designs (CRCP) are premium pavement designs that are often used on heavily-trafficked roadways and urban corridors. CRCP designs have no regularly spaced transverse joints, but contain a significant amount of longitudinal steel reinforcement (typically 0.6 to 0.8 percent of the cross-sectional area). The high steel content both influences the development of transverse cracks within an acceptable spacing (about 3 to 6 feet) and serves to hold them tightly together (see The ABCs of Continuously Reinforced Concrete, Road Science, May 2007).

The prevalence of wide cracks in CRCP has frequently been associated with ruptured steel and significant levels of corrosion, and fiber-reinforced polymer (FRP) composite materials are one product being investigated for use in CRCP in place of traditional steel bars. FRP composites consist of a matrix of polymeric material (polyester, vinyl ester, or epoxy) that is reinforced by fibers of other reinforcing materials, typically glass, carbon, or graphite.

Advantages of FRP bars include not only their corrosion resistance, but also their high longitudinal strength, high-fatigue endurance, and lightweight. Disadvantages of FRP bars include high cost, low modulus of elasticity, and low shear strength. There are concerns associated with the potential for large crack spacings and greater crack widths, which may compromise the long-term, aggregate-interlock load transfer needed to ensure long-term performance.

Two field studies have been constructed and are being monitored to help evaluate and improve the performance of FRP-reinforced CRCP designs.v